Hearing aid housings have long been molded using acrylic resins which when cured are rigid, and hard. These housings often require extensive after the fact adjusting in response to user complaints of poor fit and/or poor performance. Complaints with this type of housing substantially increase overall production costs. Each unsatisfactory hearing aid must be reworked, replaced or the charge refunded to the user.
One of the disadvantages of rigid shell aids is that they are non-compliant and may force the user's ear canal to assume an unnatural shape in the cartilaginous region of the canal in order to achieve a seal. This in time can cause user discomfort and discourage usage of the aid.
It has now been recognized that dynamic changes in the shape of a user's ear canal as the user talks, breaths or swallows produce a situation where a rigid hearing aid housing conforms to the shape of the user's ear canal in only one state. This is the state the ear canal was in when an ear impression was taken. All other states will produce an uncomfortable fit or one that does not seal properly thereby producing feedback. Some of these issues have been addressed in a publication, CIC Handbook, Chasin, Singular Publishing Group, Inc., San Diego, 1997, pg 1–55.
A variety of solutions have addressed the fitting problem. One solution is disclosed in Yoest Patent No. 6,167,141, based on Ser. No. 09/070,124 filed Apr. 30, 1998, assigned to the assignee hereof and incorporated herein by reference. In Yoest, protrusions on a compliant body contribute to a comfortable seal with the respective ear canal.
Another prior solution combined deformable ear tips with rigid standardized housings that are to be inserted into the tips. These solutions rely on the deformable tips to compensate for differences between the user's ear canal and the shape of the housing contained within the tip.
The ear tip solution has had only limited success The thickness of the tip relative to the size of the ear canal and the size of the housing carried therein have resulted in a structure which has limited bendability when inserted into or removed from the ear canal. Thus, this solution can not be used with convoluted ear canals.
Another attempted solution uses a solid elastomeric housing which carries the audio processing circuitry and the battery. Elastomers, when cured, while solid are soft and deformable.
Known solid elastomeric housings, while deformable, are substantially incompressible. Such housings exhibit a substantially constant volume. This results in a situation where portions of the ear canal may push against portions of the elastomeric housing, deforming same. However the elastomeric material pushes back against the adjacent periphery of the ear canal, since it is substantially incompressible. This process is known to produce ear pain at times. This will come about if part of the elastomeric material is adjacent to soft tissue in the ear canal.
Solid elastomeric housings require balancing softness of material with strength. Softer elastomers have lower tensile strengths and tend to rip where they are thin. While exhibiting softness, solid elastomeric housings must still have enough strength to protect internal electrical/electronic components.
It has also been known to combine a gas containing bladder with a housing for a hearing aid. The bladder is deformable and compressible. The bladder is filed with a fluid such as ambient air.
The bladder can be filled before or after insertion. When the ear canal applies compression force to the bladder, the fluid therein will also be compressed. This compression in turn will increase the pressure applied by the fluid to the interior of the bladder, and the adjacent tissue of the user's ear canal.
For a constant temperature, reducing bladder volume by 50% produces a corresponding increase in expansion pressure within the bladder and ultimately, an increased force is applied to the ear canal. This becomes uncomfortable and unacceptable to the users.
In another attempted solution, a hollow deformable hearing aid housing has been formed of a semi-rigid material with thick enough side walls to be insertable into an ear canal without buckling. One known hearing aid with a housing as described above has been publicly marketed in the U.S.A. since 1996. In this hearing aid, the internal components, such as the output transducer, a receiver, were positioned in a gas filled interior. For example, the internal volume could be filled with ambient air.
When the housing is deformed, ambient air therein is forced from the interior. This solution provides only limited flexibility in the housing, due to the thickness of the housing. Insertion rigidity is achieved with this hearing aid as a result of the thickness of the housing. Beyond the limited flexibility, no protection was provided for the receiver and other electronic components. Hence, it was possible to easily damage these components. Finally, except for the tendency of the material to return to its initial shape, the memory of the molded housing, the housing, which was relatively thick, incorporated no force applying structure which tended to force it outward when inserted in the ear canal to provide a feedback reducing seal with the canal.
There continues to be a need for more comfortable hearing aids. Since ear canals are known to change shape and volume in response to jaw movement, it would be preferable if such changes could be responded to dynamically. In addition to comfort, there continues to be a need for hearing aids which effectively seal with the respective ear canal. It would be desirable to provide such improved functionality in either custom or standard sizes of hearing aids.